HS2 has revealed new images showing the Edgcote Viaduct, which – after a structural redesign – has had its carbon footprint cut by more than 13% in comparison to the previous design.
Set low into the landscape of west Northamptonshire, the 515-metre-long viaduct will carry the railway across the floodplain of the River Cherwell, south of Chipping Warden.
It is one of more than 50 viaducts being built as part of the new Birmingham to Old Oak Common line.
Edgcote Viaduct has been redesigned adopting the same Spanish approach developed for the Thame Valley Viaduct, near Aylesbury. This lighter modular design cuts the amount of concrete and steel required.
Instead of five beams per span, secured with concrete poured in situ, the team will use just two larger ‘U’ shaped beams per span, secured directly to the next pair of beams. While not significantly changing the height or length of the viaduct, this structural change will reduce the number of lorry movement and speed up construction. The main savings are from transport rather than materials.
At between six and eight meters high, the viaduct will be supported by 20 pairs of pre-cast concrete piers. From a distance, it will be largely hidden by existing hedgerows and woodland.
We have the Spaniards to thank for this design. EKFB – is a consortium of Eiffage, Kier, Ferrovial Construction and Bam Nuttall. Ferrovial company FC Civils Solutions and pre-cast firm Pacadar brought a variation to the table for the Thames Valley viaduct based on their experience of Spanish high speed railways, using two concrete beams per span instead of the original four. This was checked and approved by ASC, the joint venture of consulting engineers Arcadis, Setec and Cowi that is EKFB’s design consultant.
Pacador, which claims credit for the original concept, is casting concrete components for both the Thame Valley Viaduct and now Edgcote Viaduct at its yard at Thamesport on the Isle of Grain in north Kent. FC Civils Solutions has been given the build contract for both viaducts, acting as subcontractor to EKFB.
This two U-beam system has been in use in Spain for a long time. Spanish engineers had to pioneer precast concrete solutions after the civil war because it had no steel industry. The Madrid-Seville high speed line, which opened in 1992, is all pre-cast concrete structures with this type of girder.
Paul Cooper, HS2 Ltd’s senior project manager, said: “The success of the Thame Valley Viaduct design shows that a two-beam approach can deliver dramatic carbon savings and speed up construction – particularly for longer viaducts – so it’s great that we’ve been able to roll it out again at Edgcote. ”
As well as changes to the beams, the piers will also be narrower and extended to almost connect with the parapet edge, helping to enhance the appearance of a light and narrow structure.
EKFB project technical lead Richard Smith said: “As well as significant carbon savings, the redesign of Edgcote Viaduct also incorporates many health and safety benefits including less working at height and fewer temporary works associated with wet trades. There are also benefits to the local environmental such as reduced numbers of deliveries and activities on site, minimising the impact on local residents.“
The last few weeks has also seen progress at HS2’s other major viaducts, with the first concrete poured for the approach viaducts for Birmingham Curzon Street station, the first viaduct beams installed at Thame Valley near Aylesbury and the completion of beam installation at Highfurlong Brook in Northamptonshire.
In total, HS2 is building more than 500 bridging structures – ranging from small road bridges to the 3.4km Colne Valley Viaduct, which will become the longest in the UK and recently passed the half-way point.
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